The Moon and Planets (and Some Deep Sky Object Meetings)
The moon starts this week hidden from view beside the dawn sun. It reaches solar conjunction, also known as its New Moon Phase, on Tuesday morning. The moon’s huddle with the sun leaves the night-time sky especially dark worldwide — ideal conditions for hunting dim galaxies and nebulas with binoculars and telescopes of all sizes.
The moon will return to view again starting on Wednesday evening after dusk, when its extremely slim silver crescent will set about 15 minutes after the sun. If you fail to spot the moon on Wednesday, it will become an easy target for the rest of the week while it climbs away from the sun and waxes fuller. In the northwestern sky during early evening on Thursday, the young crescent moon will sit a palm’s width to the left of very bright Venus. The pair of objects will set together about 10:30 pm local time. Look for the open star cluster Messier 35 sitting above and between them in the same binocular field of view.
On Friday, the moon will pass through the stars of Gemini (the Twins). Then, low in the western sky during late evening on Saturday, the waxing crescent moon will be situated about a palm’s width to the lower right of the large open star cluster in Cancer (the Crab) known as the Beehive. This cluster is several moon diameters across! Other names for it include Praesepe (the Manger) and Messier 44. Binoculars will show both the moon and the cluster in the same field of view. Observers in western North America will see the moon move to within a few finger widths of the cluster before moonset.
The planet Venus will continue to dominate the western evening sky this week, until it sets after 11 pm local time. Every evening, Venus’ orbital motion will lift it higher, delaying its setting time by a few minutes. The planet begins this week sitting between the stars Zeta (ζ) Tauri (on the left) and Elnath (on the right). These two stars form the horn tips of Taurus (the Bull).
Next Sunday evening, Venus will tickle the toes of Gemini, arriving within a degree to the right of the bright open star cluster designated Messier 35. The distant star cluster and nearby planet will appear together within the field of view of a low power telescope or your binoculars. Look closely — if Venus’ brilliance is overwhelming the cluster’s stars, try hiding the planet just outside the edge of your field of view. In a telescope, Venus is now exhibiting a gibbous phase, giving it a somewhat flattened appearance on the top.
This week, Jupiter is still almost exactly opposite the sun in the sky, causing it to be visible all night long and to show a disk that is brighter and larger than at any other time this year. The king of planets will already be visible in the eastern sky after sunset. It will reach its highest elevation (about three fist diameters) above the southern horizon around 12:45 am local time, and then descend into the southwestern sky as the sun rises. The bright star sitting just to the upper right of Jupiter is Libra’s (the Scales) brightest star, Zubenelgenubi. In binoculars or a small telescope, it splits into a closely spaced pair of stars.
On Sunday evening, May 13 between 9 pm and 10:49 pm, Jupiter’s moon Ganymede and its little round black shadow will cross (or transit) Jupiter’s disk. On Tuesday morning, May 15 the moon Io and its shadow will transit between 12:50 am and 3 am. Between Saturday evening at 11:15 pm and Sunday morning at 1:30 am, the moon Europa and its shadow will transit. All times are given in Eastern Daylight Time (EDT). A reasonable backyard telescope will show the black shadows, but a very good telescope is needed to see the moons, themselves.
The Great Red Spot takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. The best times to try this week are: Tuesday, May 15 at 10:17 pm, Thursday, May 17 at 11:55 pm, and Sunday, May 20 at 9:25 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone. Try to look within an hour before or after the times I’ve given.
This week, the ringed planet Saturn will start rising in the east just before midnight. You should be able to see its yellow-tinted point of light until almost 6 am, when it will sit about two fist widths above the southern horizon. On the mornings surrounding Monday, May 14, Saturn’s retrograde orbital motion westward will carry it past the bright star cluster designated Messier 22, also known as the Sagittarius Cluster. Closest approach of less than two finger widths occurs on Monday, when Saturn will be positioned directly above the cluster. Both objects will appear together in the field of view of a low power telescope or binoculars.
Reddish Mars will rise about 90 minutes after Saturn this week, which places it two fist widths to the left of, and a bit below, Saturn. Mars continues to steadily brighten and increase in size as the Earth’s faster orbit brings us closer to the red planet this summer. (We will pass it on the “inside track” in late July.)
Mars, too, has a close encounter with a distant deep sky object this week. In the southeastern pre-dawn sky on Monday morning, May 14, Mars’ eastward orbital motion will carry it to a position only 18 arc-minutes (or about 2/3 of the full moon’s diameter) below the small globular star cluster designated Messier 75. Both objects will appear together in the field of view of a telescope at medium-high power. The cluster is nearly 60 million times farther away than Mars. While the light from Mars will take only 6 minutes to arrive at your eyes, the globular cluster’s light has been travelling for 68,000 years! The best time to see this pairing is around 4 am local time, before the sky begins to grow brighter.
Astronomy Skylights for this week (from May 13th, 2018) by Chris Vaughan.